JP2002131246A - Method for calibrating imaging magnification at x-ray imager - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for calibrating an imaging magnification whereby an imaging magnification of X-ray images of a measuring object can be correctly measured using a simple operation, thereby enabling strict analysis and measurement, on the basis of X-ray radiographic images and X-ray tomographic images. SOLUTION: A jig of a known size is placed on a measurement stage, and the imaging magnification is obtained from the X-ray radiographic image of the jig. Similarly, the imaging magnification is obtained from the X-ray radiographic image, after the measurement stage 13, is moved by Δd. A distance Di, between a focal point of an X-ray source 1 and a light-receiving face of an X-ray detector 2, and distances D1 and D2 between the focal point 1a of the X-ray source 1 and positions of the measurement stage, before and after being moved by Δd; can be calculated correctly through geometric calculations by correctly measuring the movement amount Δd. Even if the measurement stage 13 or the X-ray detector 2 is moved closer to or separated from the X-ray source 1 afterwards, the correct imaging magnification can be obtained, by using the calculation results so long as the movement amount can be measured correctly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for analyzing and measuring the internal shape of a measurement object (subject).
The present invention relates to a method for calibrating an imaging magnification performed in an X-ray imaging apparatus such as an X-ray fluoroscope and an X-ray tomographic imaging apparatus in order to accurately determine an imaging magnification.

[0002]

2. Description of the Related Art Generally, in an X-ray imaging apparatus such as an X-ray fluoroscope or an X-ray tomographic imaging apparatus, strict analysis or measurement based on an image taken unless the imaging magnification is accurately determined. Can not do.

In a conventional X-ray imaging apparatus, the distance Do between the position of an X-ray source and an object to be measured (hereinafter, referred to as a subject), the position of the X-ray source and the image tube or the like which is an image receiving unit. The distance Di from the position of the X-ray detecting means is measured by a servomotor, an encoder, a measure, or the like, and the magnification R is calculated by R = Di / Do.

[0004]

However, with the above-described conventional calculation method of the imaging magnification, an accurate imaging magnification cannot be obtained. The reason is that "X" for obtaining the distances Do and Di used in the above-described conventional calculation method is "X".
This is because the position of the radiation source and the position of the X-ray detecting means include uncertain elements.

That is, the “position of the X-ray source” used in the above calculation indicates the focal point of the X-ray,
The focal point of the X-rays is inside the X-ray generator, and how much the actual focal point is from the X-ray irradiation port of the X-ray generator depends on the assembly accuracy of the X-ray generator and the X-ray generation conditions. It can vary depending on various factors. In addition, as for the "position of the X-ray detecting means" used in the above-mentioned conventional calculation, the light-receiving portion (X-ray sensitive surface) is also concave or concave, so that the position of the X-ray detecting means is determined everywhere. Is uncertain. For this reason, the imaging magnification determined by the conventional method must be said to be inaccurate.

The present invention has been made in view of such a situation, and it is possible to accurately obtain an imaging magnification in an X-ray fluoroscope or an X-ray tomographic imaging apparatus. It is an object of the present invention to provide a method of calibrating an imaging magnification that enables accurate analysis and measurement.

[0007]

In order to achieve the above object, a method of calibrating an imaging magnification in an X-ray imaging apparatus according to the present invention comprises an X-ray source, an X-ray to which X-rays from the X-ray source are incident. Detecting means, provided between the X-ray source and the X-ray detecting means,
A measuring table having at least a moving mechanism in a direction connecting the two, a length measuring means for measuring a moving distance of the measuring table by the moving mechanism, and a measuring table mounted on the measuring table by using an output of the X-ray detecting means. A method of calibrating an imaging magnification in an X-ray imaging apparatus including an image processing means for constructing an X-ray fluoroscopic image of a subject, wherein the measurement is performed while a jig of a known size is placed on the measurement table. The table is moved in the direction connecting the X-ray source and the X-ray detection means, and the imaging magnifications kR1 and kR2 of the X-ray fluoroscopic image of the jig before and after the movement, or the imaging magnifications R1 and R2 on the X-ray detection means. And the distance Di between the focal point of the X-ray source and the light receiving surface of the X-ray detection means, and the distance between the focal point of the X-ray source and the jig on the measuring table at the position P1 before the movement using the moving distance Δd of the measuring table. At the distance D1 or at the position P2 after movement with the X-ray source It calculates the eggplant distance D2 between the jig on the weighing platform, characterized by storing or recording them as data for the calculation of the imaging magnification at an arbitrary position of the measuring table.

The present invention makes it possible to accurately determine the imaging magnification by a simple operation using a jig, and to fix the positions of the X-ray source and the X-ray detection means while fixing the positions thereof. Place a jig of known dimensions on the measuring table between
The distance between the X-ray source and the X-ray detection means is calculated as follows by moving the X-ray source and the X-ray detection means in a direction connecting the X-ray source and the imaging magnification R1 and R2 before and after the movement. Di, the distance D1 between the jig on the measuring table and the X-ray source at the position P1 before the movement, or the position P2 after the movement
The distance D2 between the jig on the measuring table and the X-ray source can be calculated by a simple geometrical operation described below, and the position of the X-ray source and the X-ray detection means can be calculated by using the calculation result. As long as is not greatly changed or the measuring table is not largely moved, an accurate imaging magnification of the subject can be obtained, and by performing this calibration as needed, an accurate imaging magnification can always be obtained.

The principle of the present invention will be described below with reference to FIG. The distance between the focal point 1a of the X-ray source 1 and the light receiving surface 2a of the X-ray detection means 2 is Di (unknown), and a measuring table 3 for placing a subject W therebetween is arranged. Is movable in the direction connecting the X-ray source 1 and the X-ray detection means 2 and the movement distance can be accurately measured by the length measuring means. The initial position of the measuring table 3 is P1, and the distance between the position P1 and the focal point 1a of the X-ray source 1 is D1 (unknown). Further, a position when the measuring table 3 is moved from the position P1 by Δd in the direction of the X-ray detecting means 3 is defined as P2, and a distance between the position P2 and the focal point 1a of the X-ray source 1 is D2 (unknown). And

The X-ray fluoroscopic image of the subject W formed on the monitor screen based on the output of the X-ray detecting means 2 is k times the image of the subject incident on the light receiving surface 2a of the X-ray detecting means 2. The size of the X-ray fluoroscopic image of the subject W on the monitor screen and the actual size of the subject W become the imaging magnification.

Now, when an X-ray fluoroscopic image on the monitor screen 4 is obtained by using a jig of known dimensions as the subject W and placing it on the measuring table 3 located at P1, the magnification is assumed to be kR1. In this state, the image on the light receiving surface 2a of the X-ray detecting means 2 is R1 times the actual size L of the subject W. Next, when the measuring table 3 is moved by Δd from that state and is positioned at P2, assuming that the imaging magnification is kR2, the image on the light receiving surface 2a of the X-ray detecting means 2 is also a jig. R2 times the actual size L.

The movement amount Δd of the measuring table 3 can be accurately measured by the length measuring means as described above.
1 and kR2 can be easily known from the size of the X-ray fluoroscopic image on the monitor screen and the known dimension L of the jig. Further, k can be grasped in advance as a device constant. R2 can also be easily known. Then, by using these known numerical values Δd and R1 and R2, the distance Di between the focal point 1a of the X-ray source 1 and the light receiving surface 2a of the X-ray detecting means 2 and the parfocal point 1a are calculated as follows. Can be calculated from the positions P1 and P2.

That is, in FIG. 1, D1 · R1 = Di D2 · R2 = Di D2 = D1 + Δd.

D1 = Δd · R2 / (R1−R2) (1) D2 = Δd · R1 / (R1−R2) (2) Di = Δd · R1 · R2 (R1−R2) ) (3) can be calculated.

By using the above Di and D1 or D2, the imaging magnification can be accurately calculated.
That is, for example, when the position of the measurement table 3 is used with P2 as a reference, the measurement target is placed on the measurement table 3 at the position P2, and the measurement table 3 is set to an appropriate size on the monitor screen.
Assuming that the amount of movement read by the length measuring means is ΔD when the light-receiving surface 2a of the X-ray detecting means 2 is moved.
The magnification Rx of the upper image with respect to the actual size of the measurement object can be accurately obtained by the following formula: Rx = Di / (D2 + ΔD) (4), and the imaging of the X-ray fluoroscopic image of the measurement object on the monitor screen The magnification can be accurately obtained as kRx by multiplying the ratio k described above. Also, X
In a device in which the X-ray source 1 and the X-ray detection means 2 can be relatively moved, for example, in a device in which the X-ray detection means 2 can be moved in a direction approaching or separating from the X-ray source 1, a measuring table 3
Similarly to the above, the moving amount of the X-ray detecting means 2 can be accurately measured by providing the length measuring means, and by adding or subtracting the moving amount to or from Di, the X-ray detecting means 2 can be measured. Even if is moved, an accurate imaging magnification can be obtained.

Further, as described above, the subject W
A jig is arranged, and an X-ray fluoroscopic image is observed in a state where another jig is arranged in close contact with the light receiving surface of the X-ray detecting means 2, and the jig on the measuring table 3 is closely attached to the light receiving surface. Jig X
From the difference in the sizes of the fluoroscopic images, the imaging magnifications R1 and R2 on the light receiving surface of the X-ray detection means of the jig on the measuring table 3 can be directly known, and the magnifications R1 and R2 are obtained using this method. Even if R1 and R2 are substituted into the above equations (1) to (3), the same operation and effect can be obtained, and the present invention also includes this method.

The calculation of the imaging magnification as described above is performed by X
The present invention can be equally applied to both a fluoroscopic apparatus and an X-ray tomographic imaging apparatus.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram showing a configuration of an X-ray imaging apparatus to which the method of the present invention is applied.

The apparatus in this example is an X-ray fluoroscope, which comprises an X-ray source 11 and an X-ray detector 12 arranged opposite thereto, for example an image intensifier and a CCD. The measurement table 13 includes a calculation / control device 15 having an image processing function of constructing an X-ray fluoroscopic image of the measurement object using the pixel output from the X-ray detector 2 and displaying the image on the display device 14. I have. The measuring table 13 can be moved in a direction connecting the X-ray source 11 and the X-ray detector 12 by a driving mechanism 13a, and the amount of movement is detected every moment by a linear encoder 13b. It is captured. Further, the X-ray detector 1
2 can be moved in the direction of approaching / separating from the X-ray source 11 by the drive mechanism 12a, and the amount of movement is also momentarily detected by the linear encoder 12b and taken into the arithmetic / control device 15. It is. The arithmetic and control unit 15 calculates the distance between the X-ray source 11 and the X-ray detector 12 and the distance between the X-ray source 11 and the measuring table 1 based on the outputs of the linear encoders 12b and 13b.
3 is displayed on the display device 14 every moment.

Now, in the above device, the display device 14
Is the distance between the X-ray source 11 and the X-ray detector 12 and the distance between the X-ray source 11 and the measuring table 13
As described above, the distance between the focal point of the X-ray source 11 and the light receiving surface of the X-ray detector 12 and the distance between the focal point and the measuring table 13 are not accurately represented, and include uncertain elements, and If used as it is, an accurate imaging magnification cannot be obtained. Therefore, the following calibration operation is performed.

A jig 20 as shown in the front view of FIG. 3 is prepared for calibration of the imaging magnification. The jig 20 is formed by forming two marks 22a and 22b at predetermined intervals, for example, precisely 10 mm, on an acrylic plate 21, and the marks 22a and 22b are formed on the acrylic plate 21.
It is formed by carving a thin shallow groove and bonding it with lead powder embedded in it.

In the calibration operation, the position of the X-ray detector 12 is fixed, and the measuring table 13 at an arbitrary position is set.
The jig 20 is set on the upper side so that the spreading direction of the marks 22 a and 22 b is orthogonal to the optical axis of the X-ray, and the X-ray fluoroscopic image is displayed on the display device 14. By measuring the distance between the marks 22a and 22b in the X-ray fluoroscopic image at that time, the imaging magnification kR1 in that state is measured. Next, the measurement table 3 is moved by an appropriate amount in a direction away from the X-ray source 11. The X of the measurement table 13 displayed on the display device 14 based on the output of the linear encoder 13b
The displayed value of the distance from the radiation source 11 does not accurately represent the distance from the X-ray focal point, but the moving amount Δd of the measuring table 13 can be accurately known from the difference between the displayed values before and after the movement. . Then, after moving by Δd, the distance between the marks 22a and 22b in the X-ray fluoroscopic image of the jig 20 displayed on the display device 14 in that state is measured, and the imaging magnification kR2 is measured.

Next, using the ratio k (known) of the size of the image formed on the light receiving surface of the X-ray detector 12 to the size of the image on the screen of the display device 14, the imaging magnification before and after the movement is determined. k
From R1 and kR2, magnifications R1 and R2 on the light receiving surface of the X-ray detector 12 before and after the movement of the measuring table 13 are obtained.

By the above operation, the distance D1 from the focal point of the X-ray source 11 to the measuring table 13 (the jig 20) before moving, and X
The distance D2 from the focal point of the X-ray detector 12 to the light receiving surface of the X-ray detector 12 and the distance Di from the focal point of the X-ray source 11 to the light receiving surface of the X-ray detector 12 are described in (1) to (3) above. It can be calculated accurately using the equation.

By storing or recording this Di and D1 or D2, as long as the measuring table 13 or the X-ray detector 12 is not largely moved, even if these are moved to an arbitrary position, even the amount of movement thereof. By accurately measuring with the linear encoders 12b and 13b, when the measurement target whose dimensions are unknown is placed on the measurement table 13 and its X-ray fluoroscopic image is displayed on the display device 14, the accurate imaging magnification is obtained. Can be requested. Specifically, for example, when only the measurement table 13 is moved to the X-ray detector 12 side by ΔD in a state where the calibration operation is performed, the display device 14 is obtained from the above equation (4) and the above ratio k. The imaging magnification on the screen can be accurately obtained. When the X-ray detector 12 is moved by ΔD ′ in a direction away from the X-ray source 11 without moving the measurement table 13 in a state where the calibration operation is performed, Rx ′ = (Di + ΔD ′) / D2 · (5), the magnification on the light receiving surface of the X-ray detector 12 is obtained, and by multiplying by k, the imaging magnification on the screen of the display device 14 can be obtained.

Here, in the above description, the jig 20 displayed on the screen of the display device 14 in the calibration operation is described.
Jig 2 by measuring the size of the X-ray fluoroscopic image of
Although the imaging magnifications kR1 and kR2 of 0 have been obtained, the magnifications R1 and R2 of the image on the screen of the display device 14 of the jig 20 can be obtained by the following method.

That is, in addition to the jig 20 shown in FIG. 3, a jig 30 as shown in a front view in FIG. 4 is used. This jig 30 has an acrylic plate 31 as a base similarly to the jig 20, and has a plurality of marks 32a, 32b, 32c on its surface.
The pitch between adjacent marks is equal to the pitch between the marks 22a and 22b of the jig 20, for example, 10 mm. Each mark 32a, 32b, 32c,... Of the jig 30 has a shallow groove formed on the surface of the acrylic plate 31 and has a lead powder inside the same as the marks 22a, 22b of the jig 20. Are embedded and bonded, and the width is larger than the marks 22a and 22b.

By using the jig 30, the jig 20 can be easily set on the light receiving surface of the X-ray detector 12 without measuring the size of the X-ray fluoroscopic image of the jig 20 on the screen of the display device 14. The magnifications R1 and R2 of the image of the tool 20 can be obtained.

That is, in the calibration operation, as shown in FIG. 5, the jig 20 is placed on the measuring table 13 and the jig 30 is brought into close contact with the light receiving surface of the X-ray detector 12, as in the previous example. And fix it. In this state, when the X-ray source 11 is driven to generate X-rays, the jig 20 on the measurement table 13
The distance between the focal point of the X-ray source 11 and the light receiving surface of the X-ray detector 12,
And an image is formed on the light receiving surface of the X-ray detector 12 under a magnification corresponding to the distance between the focal point of the X-ray source 11 and the jig 20,
The image of the jig 30 closely attached to the light receiving surface of the X-ray detector 12 forms an actual size image on the light receiving surface.

Therefore, the observation table 13 is appropriately moved while observing the X-ray fluoroscopic images of the jigs 20 and 30 on the screen of the display device 14, and firstly, on the light receiving surface of the X-ray detector 12 of the jig 20. The measuring table 13 is stopped at a position where the magnification of the image at the point has become a first specified integral multiple, for example, four times. The fact that the imaging magnification has become an integer multiple means that both the images of the marks 22a and 22b of the jig 20 are displayed on the marks 32a, 32b and 32c of the jig 30 as illustrated in the screen of the display device 14 in FIG. ...
6A shows a state where the magnification is quadrupled, and FIG. 6B shows a state where the magnification is tripled.

Next, the measuring table 3 is moved to the X-ray detector 12 side, and measurement is similarly performed at a position where the imaging magnification of the jig 20 is a second integral multiple, for example, 3 times. The platform 13 is stopped. Then, the linear encoder 13 before and after the movement
From the output of b, the movement amount Δd is accurately known, and in the above-described equations (1) to (3), the first integer multiple is R1 and the second integer multiple is R2, and the focal point of the X-ray source 11 and the position before the movement are determined. D1 between the measurement table 13 and the X-ray source 11 and the measurement table 1 after the movement
3 and the distance Di between the focal point of the X-ray source 11 and the detection surface of the X-ray detector 12 are determined. By storing or storing these, the object to be measured is placed on the measuring table 13 and the measuring table 13 or the X-ray detector 12 is
The imaging magnification on the screen of the display device 14 when is arbitrarily moved can be accurately obtained by obtaining Rx or Rx ′ using the formula (4) or (5) and multiplying by the constant k. .

The shape and structure of the jig 20 or 30 used in each of the above-described examples of the calibration operation are not particularly limited, and have the functions evident in the above description. Any shape, any shape
Needless to say, a structure can be used.

In the above, an example in which the present invention is applied to an X-ray fluoroscopic apparatus has been described. However, an X-ray tomographic image imaging apparatus (CT apparatus) can also be realized by using the imaging function of the X-ray fluoroscopic image. The imaging magnification can be accurately obtained based on the same calibration operation as in each of the above examples.

[0034]

As described above, according to the present invention, an X-ray fluoroscopic image is obtained by mounting the measuring table to two places by using a simple jig and moving the measuring table to two locations. The distance between the focal point of the X-ray source and the light receiving surface of the X-ray detector and the distance between the focal point of the X-ray source and the measuring table can be accurately obtained by a simple calculation. Or, even if the measuring table is moved appropriately, as long as it has a function of accurately measuring the amount of movement, the imaging magnification of the measuring object can be accurately obtained, and the X-ray fluoroscopic image of the measuring object can be obtained. Or, strict analysis or measurement based on tomographic images can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a block diagram showing an example of the configuration of an X-ray imaging apparatus capable of calibrating an imaging magnification by applying the method of the present invention.

FIG. 3 is a front view showing a configuration example of a jig used for an example of an imaging magnification calibration operation to which the method of the present invention is applied.

FIG. 4 is a front view showing a configuration example of a jig used in combination with the jig 20 of FIG. 3 in another example of the operation of calibrating the imaging magnification to which the method of the present invention is applied.

FIG. 5 is an explanatory diagram of a calibration operation of an imaging magnification using the jigs 20 and 30 of FIGS. 3 and 4;

6 is an explanatory diagram of a method of knowing an image magnification on a light receiving surface of the X-ray detector 12 of the jig 20 from a screen of the display device 14 in the calibration operation of FIG. (B) is a figure which shows the state which tripled.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 X-ray source 12 X-ray detector 12a Drive mechanism 12b Linear encoder 13 Measuring stand 13a Drive mechanism 13b Linear encoder 14 Display device 15 Operation / control device 20 Jig 21 Acrylic plate 22a, 22b Mark 30 Jig 31 Acrylic plate 32a, 32b, 32c mark

Claims (1)

[Claims] An X-ray source, X-ray detecting means for receiving X-rays from the X-ray source, and an X-ray source provided between the X-ray source and the X-ray detecting means, at least in a direction connecting the two. A measuring table provided with a driving mechanism, length measuring means for measuring a moving distance of the measuring table by the driving mechanism, and an X-ray fluoroscopic image of a subject placed on the measuring table using an output of the X-ray detecting means A method for calibrating an imaging magnification in an X-ray imaging apparatus having image processing means for constructing a measurement table, comprising: mounting a jig of known dimensions on the measurement table; The detecting means is moved in the direction connecting the detecting means, and the imaging magnification kR of the X-ray fluoroscopic image of the jig before and after the movement is obtained.
1, kR2, or imaging magnification R on X-ray detection means
The distance Di between the focal point of the X-ray source and the light receiving surface of the X-ray detecting means, the focal point of the X-ray source, and the position P1 before the movement on the measuring table using R1, and the moving distance Δd of the measuring table. The distance D1 between the jig and the distance D2 between the X-ray source and the jig on the measurement table at the moved position P2 is calculated, and these are used to calculate the imaging magnification at an arbitrary position on the measurement table. A method of calibrating an imaging magnification in an X-ray imaging apparatus, which is stored or recorded as data.